Polyionic molecules are synthesized and naturally occurring compounds and are widely used across a range of applications including rheology modifiers, cosmetics, water treatment and nutrition applications. Polyionic molecules include polyelectrolytes, such as positively charged polycations, negatively charged polyanions, or zwitterionic polymers, as well as other polyionic species including metal oxide nanoparticles, metal sulfide nanoparticles, or functionalized nanoparticles. Some polyionic molecules include hydrogen donors and acceptors. Some polyionic compounds are used in methods for forming coatings, such as by Layer-by-Layer deposition methods.
Layer-by-Layer (LbL) processes typically build films making use of charge-charge, hydrogen bonding, or other complementary interactions to assemble successive layers. This typically requires the use of solvents to ionize molecules or support hydrogen donation and acceptance in the deposition solutions. While it is possible to use alcohols, glycols, and other organic solvents, water is the solvent of preference due to its low cost and low toxicity. This is particularly true for spray LbL where it is undesirable to aerosolize organic solvents. The use of water as solvent means that the scope of materials that can be used in traditional LbL and similar methods is restricted, and that the resulting product coatings are limited in their performance and range of properties.